Sea to Summit Spark Ultralight Sleeping Bag 18

The Sea to Summit Spark Ultralight Sleeping Bag 18 is a unisex mummy bag filled with 850+ FP goose down treated with Ultra-Dry Down, built for demanding three-season ultralight trips. A -2°C comfort rating, -8°C limit, and -26°C extreme give it decent temperature margin for cooler autumn or early-spring nights. The 430g fill is arranged in horizontally-oriented box baffles — a more complex and costly construction than sewn-through seams, but more effective at preventing down shift and cold spots. A 10D nylon shell and 7D nylon liner rank among the thinnest fabrics used in this category, and combined with a contoured hood, draft collar, and draft tube, they help keep total weight to 618g. A fill efficiency of 12.9g per degree and a 3.7L packed volume point to a bag built primarily around minimising pack weight — a strong pick for thru-hiking and long trips where every gram of base weight counts, less so where the priority is durability under rough handling.